Recognizing faults

1
Recognizing faults

• Practice with
• thrust faults and
• normal faults

2
Why study faults?

• Classification of faults
• - each type of fault forms under different
  geologic conditions
• - so, if we can characterize the nature of the
  fault, we can conclude something about the
  geologic history...

3
Some faults are easy to see

• A Normal fault

The San Andreas fault - a slip fault
4
Some are harder to see an extensional fault

• The fault is here
• lt(normal fault)

lt The level land has dropped DOWN
5
Orientation of fault surfaces
Strike and Dip

Note for mechanical reasons fault planes are
seldom planar over long distancesthus, we must
take MANY strike and dip measurements along a
fault.
6
The Nature of Fault Shapes

• Faults are not infinite
• Faults can be irregularly shaped

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Strike Slip Fault
8

• http//earthobservatory.nasa.gov/Study/denali/

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Compression
Oldest fault
Newest fault
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Compression

• A thrust fault showing how layers have moved.
  (black is a layer of coal)

Hanging wall
Foot wall
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Compression Distortion along a fault

• Movement drags on the rock next to this thrust
  fault.
• The layers
• became bent
• when the walls
• moved.

Hanging wall
Foot wall
Fault
12
Extensional faults (Utah)
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Extension

• An area of extension is called Basin and Range
  topography.
• (the flat areas are basins, the mountains are
  ranges)

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Extension

• The fault line is here

Hanging wall
This lower area has dropped down lt
Foot wall
15
Extension

• Normal faults

Foot wall
Hanging wall
Foot wall
Notice this broken layer has moved down.
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Extension

• Can you see a normal fault in this picture?

Hanging Wall
The black shale layer has dropped down compared
to the other side.
Foot Wall
http//raider.muc.edu/mcnaugma/structur.htm
17
1 Is this a normal or thrust fault?
Hanging wall
Foot wall
http//virtual.yosemite.cc.ca.us/ghayes/Death_Vall
ey_Friday.htm
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2 Is this a normal or thrust fault?
Hanging wall
(Same layer)

• Foot wall

http//raider.muc.edu/mcnaugma/structur.htm
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3 Is this a normal or thrust fault?
Hanging wall
(older rock)
(younger rock)
Foot wall
http//raider.muc.edu/mcnaugma/structur.htm
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4 Normal or Thrust fault?
www.pitt.edu/.../7Structures/NormalFaults.html
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5 Normal or thrust fault?
http//gpc.edu/pgore/geology/geo101/faults.htm
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6 Thrust or Normal faults?